The present invention relates generally to an optical system used with imaging apparatus or the like, and more particularly to an imaging optical system well fit for a single focus interchangeable lens in a mirrorless type camera as well as an imaging apparatus incorporating the same.
So far, there has been an imaging optical system known in the art, which keeps its full length constant, makes use of an inner focus mode, and works in favor of dustproofing and sound-proofing. The imaging optical system set forth typically in JP(A) s 11-160617 and 2005-321574 is comprised of, in order from its object side, a first lens group of positive refracting power, a second lens group of negative refracting power, an aperture stop and a third lens group of positive refracting power, wherein the first and third lens groups remain constantly fixed, and the second lens group of negative refracting power is moved toward the image side upon focusing from a far distance to a near distance. This makes the optical system more favorable for dustproofing and soundproofing, and permits it to have much higher optical performance as well.